I have been having a really tough time figuring out how to make a blinking light in blender. In the attached blend file I have an issue that I really need help resolving!
The object in the the blend has three parts a bottom and blob like middle and the light at the front. When I render the animation rather than look like a blinking light at the front, the light causes some really awkward global effects. Notice how the bottom part of the object seems to change color. In general I want the blinking light to be constrained to the bulb area. I am imagining a red light on a control board if you know what I am saying. The light needs to go on and off but the light emitted should be relatively constrained to the bulb area. I have spent considerable time working on this, and even posted files to this board before. PLEASE, any help is greatly appreciated!!!
Your scene is changing color because there is a big black shadow from your main light (“Lamp”). When secondary (blue, “Point”) light is on, it gives the shadow a blue color.
In real life there are no such lights that give perfect black shadows (real lightsources have non-zero size, light bounces off the objects and lights up the shadows, and there is almost never only one light in the scene).
Now, answering your question on how to restrict the influence distance of the light—simply turn on the Sphere option in the light settings. Anyway, it will not help your black shadows.
What I would suggest you is to read the Blender manual first, the chapter about lights, and get some knowledge (there is a lot of articles on the internet) in the subject. Believe me, it will help you a lot in the future if you want to continue learning 3d.
What I did, back in my BI days (the only reason for me to go back to BI from cycles would be for SSS and volume) was adding an hemi lamp, of the same color of the main lamp, to light the shadows a bit.
Of course there are better ways to increase realism, but for a quick solution that is good enough.